Facebook takes issue with their use of the word “book” which, according to the lawsuit, they claim infringes on their brand.

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"If others could freely use 'generic plus BOOK' marks for online networking services targeted to that particular generic category of individuals, the suffix BOOK could become a generic term for 'online community/networking services' or 'social networking services,' " Facebook argued in the lawsuit, which was filed in San Jose district court. "That would dilute the distinctiveness of the Facebook Marks."

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Teachbook, which has been in development since early 2009, hasn’t launched yet. Since filing for a trademark application in March 2009, the start up has been working with Facebook to circumvent the issue, but now that the multi-billion-dollar company has brought legal action, principals with the company say they’ll fight.

"We've been sitting here scratching our heads for the last couple of days," Shrader told the Chicago Tribune. "We're trying to understand how Facebook, a multi-billion dollar company, feels this small enterprise in Chicago is any type of threat."